Micro-electromechanical (MEMS) sensors constitute an enabling technology that provides a means for measuring physical quantities such as acceleration, pressure, sound, temperature and the like. Such measured physical quantities supplied by MEMS sensors are often used to provide feedback for advanced system controls such as used in jet engines and smart phones. Further, MEMS sensors are used across many industries such as consumer electronics, manufacturing, aerospace, automotive and medical sensing applications.
An ever-persistent objective in many industries that use MEMS sensors typically includes reducing device size while improving performance. Further, the ability to achieve this objective becomes even more challenging as technology matures. MEMS sensors are no exception. One of the most common MEMS sensors is an accelerometer. A state-of-the-art MEMS accelerometer such as used in consumer electronics typically incorporates a capacitive transduction mechanism. A typical MEMS accelerometer features a suspended mass that moves with applied acceleration, where the acceleration is quantified through the change in capacitance between suspended fingers and stationary, comb-drive fingers.
There are several major drawbacks to these state-of-the-art MEMS accelerometers. For example, typical MEMS accelerometers have an inherent scaling limitation due to the resolution of the sensing mechanisms employed. The most commonly employed sensing mechanism in MEMS accelerometers is the capacitive detection mechanism, typically with comb drive fingers or parallel plate capacitors. The typical size of the sensing section alone of a MEMS accelerometer is ˜700 μm by ˜700 μm, which is fabricated next to the required signal conditioning circuitry bringing the total device size to ˜2 mm by ˜2 mm. A MEMS microphone may be on the order of ˜1 mm by ˜1 mm, not including the separate signal conditioning circuit. These capacitive based devices, in addition to piezoresistive, piezoelectric, and optical transduction mechanisms, are not scalable into the nanometer regime because the dynamic range is directly dependent upon the sensor area in addition to other limitations in fabrication and sensitivity (i.e., resolution). In other words, reducing the device size may result in significant reduction in sensor output.
Another significant drawback is the difficulty in CMOS integration. Though it is desirable to have necessary circuits underneath the MEMS structure, typical MEMS accelerometers and microphones are fabricated separately from the circuit die and combined during packaging. Accordingly, incompatible fabrication steps may exist between the two.
Lastly, such large MEMS devices typically possess low resonant frequencies, which limit their linear frequency range, and hence the frequency ranges for input signals. Accordingly, there is a need for improved techniques to allow for further scaling and CMOS integration of MEMS sensors such as accelerometers. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and claims, taken in conjunction with the accompanying figures and the foregoing technical field and background.